There already exist a certain number of devices for the bending testing of test pieces and which mainly include a test piece support structure secured to a base and provided with two rollers on which the test piece extremities are laid, and a pin sliding with respect to one portion of the base perpendicular to the test piece on which it is pressed halfway between the supports. It is then possible to conduct conventional tests for measuring the force on rupture or measure bending according to the force applied to the pin.
Some of these devices are completed by a chamber surrounding the test piece and the pin, this making it possible to test in special conditions the temperature, atmosphere, etc., but tests conducted at extremely low temperatures require that the test piece be immersed into a cryogenic liquid, such as liquid nitrogen, which poses new problems in this field as it becomes difficult or impossible to measure the bending of the test piece by conventional methods with stress gauges or with direct reading, the use of the cryogenic fluid rendering handlings of the device as being scarcely practical. If, for example, it is desired to carry out several successive tests, it is impractical to on each occasion empty the liquid contained in the chamber so as to fill it again as soon as the test piece is replaced.